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5310 |
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Isothermal and cyclic oxidation of CGS and HVOF iron aluminide coatings |
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Nuria Cinca* / University of Barcelona, Spain RALUCA Pflumm/ DECHEMA-Forschungsinstitut.Hochtemperaturwerkstoffe. , GERMANY MARIO Rudolphi/ DECHEMA-Forschungsinstitut.Hochtemperaturwerkstoffe. , GERMANY MATHIAS Galetz/ DECHEMA-Forschungsinstitut.Hochtemperaturwerkstoffe. , GERMANY SERGI Dosta/ Thermal Spray Centre (CPT). Universitat de Barcelona. , SPAIN IRENE G. Garcia Cano/ Thermal Spray Centre (CPT). Universitat de Barcelona. , SPAIN JOSEP M. Guilemany/ Thermal Spray Centre (CPT). Universitat de Barcelona. , SPAIN |
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Intermetallic transition metal aluminides are excellent candidates for use in high temperature component design due to their high-temperature strength and superior oxidation resistance, providing not only longer equipment service life, but also the potential to increase the operating temperatures. In spite of their good high-temperature corrosion resistance especially the Fe-Al based bulk alloys have limited or poor mechanical strength at high temperatures. Therefore, aluminides appear particularly interesting as coatings or claddings on more conventional higher-strength materials which are less corrosion-resistant at high temperatures. Although high temperature performance has been studied for Fe-Al-bulk alloys in more detail, systematic investigations of the oxidation behavior of coatings under isothermal and cyclic conditions are scarce. The present work presents the oxidation behavior at 900ºC of Fe-Al-coatings (40at.%Al) produced by high velocity oxygen fuel spraying (HVOF) and cold gas spraying (CGS), respectively. By spraying with the CGS technology, the presence of Al-depleted areas is avoided, as well as the highly heterogeneous structure that can be observed when spraying with HVOF; in both cases, the spraying conditions were previously optimized to achieve high efficiencies with the lowest porosity and intersplat oxidation as possible. Despite the low ductility of such near stoichiometric composition, dense coatings have been obtained by CGS, preserving the ordered crystalline structure and sufficient Al content to form protective alumina layers. First, we present results related to the corrosion mechanism of these coatings performed in laboratory air at 900°C. The duration of the tests was up to 300 h for both isothermal and cyclic exposure. Second, we present first results on the mechanical behaviour of such coatings, determined via four point bending tests performed on as sprayed samples. Particular attention is given to the influence of the spraying method on the observed degradation mechanism of the investigated coatings. |